Characterized by being self-renewing, undergoing differentiation and being immortal, stem cells have been proposed to be a solution for the problems of regenerative medicine and tissue replacement so that they can be used to treat various degenerative diseases as well as to provide deep insight into cellular biology. Adult stem cells, obtainable from various tissues, are far more attractive than embryonic stem cells because of the ability to come from an unlimited number of sources and the ethical objections to using human embryos as a source of cells are rendered irrelevant. Moreover, stem cells isolated from umbilical cord blood have advantages over other adult stem cells in that the donors of umbilical cord blood are not injured, unlike the donors of bone marrow or adipose tissue.
Umbilical cord blood-derived mesenchymal stem cells have been successfully introduced into various kinds of cells including neural cells, hepatocytes, osteocytes, etc., in vitro (Sun, W. et al., Stem cells, 23:931, 2005; Hong S H. et al., Biochem. Biophys. Res. Commun., 30:1153, 2005; Hutson E L. et al., Tissue Engineering, 11:1407, 2005). Successful in vivo transplantation of umbilical cord blood-derived mesenchymal stem cells for injuries, diabetes mellitus and heart infarction were also reported (Nonome, K. et al., Am, J. Physiol. Gastrointest. Liver Physiol., 289:1091, 2005; Yoshida, S. et al., Stem cells, 23:1409, 2005; Kim Bo. et al., Circulation, 112:96, 2005). Due to the low possibility of infectious diseases being transmitted and the low possibility of causing graft-versus-host diseases, the transplantation of umbilical cord blood-derived mesenchymal stem cells has been increasingly applied to both child and adult patients (Claudio G. B. et al., Annual Review of Medicine, 57:403, 2006). Although umbilical cord blood transplantation has been accepted as a therapy for some diseases, particularly hematopoietic defection-related diseases (Grewal, S S. et al., Blood, 103:1147, 2004; Knutsen, A P. et al., Journal pediatrics, 142:519, 2003; Ooi, J. et al., Blood, 103:489, 2004; Sanz G F. et al., Blood, 103:489, 2004), studies on the clinical application of umbilical cord blood-derived mesenchymal stem cells are still limited. For example, there are reports on stem cells being used to successfully cure, not completely but partially, women having spinal cord injuries and patients with Buerger's disease (Kim, S W. et al., Stem Cells, 2006; Kang, K S. et al., Cytotherapy, 7:368, 2005). However, the mechanism of development of the cells or how to grow and proliferate them still remains unknown.
It is difficult to isolate mesenchymal stem cells from umbilical cord blood. For example, when the method used to isolate bone marrow-derived mesenchymal stem cells is applied to umbilical cord blood, the isolation rate remains at around 20%. As much as 50% of the mesenchymal stem cells may be isolated from flesh blood which has been taken 5 hours before the isolation. However, the isolation rate is decreased to 20% or less when the blood has been taken over 5 hours before doing the isolation and the cells, although isolated, do not proliferate well.